The present invention relates to a device for frequency conversion of a laser by means of one or more non-linear crystals arranged in the laser beam, into which the required power density is introduced by an arrangement in the area of the narrow point of an associated focusing lens system, with a collimator that minimizes the divergence of the laser beam, and with an optical beam converter that shapes the cross section of the laser beam.
Published international patent application no. WO 00/03293 discloses a device for the frequency conversion of the light of a laser in which a non-linear crystal is arranged in the laser beam, into which the required power density is introduced by an arrangement in the area of the narrow point of a focusing lens system, and with a collimator that minimizes the divergence of the laser beam.
U.S. Pat. No. 5,848,079 (=DE 195 27 337) further discloses the arrangement of several non-linear crystals in a device for the frequency conversion of the light of a laser, in which focusing lens systems or a polarization rotator are arranged, respectively, between the crystals. If focusing lens systems are associated with the crystals, the corresponding design requires a relatively long overall length.
In principle, it is also already known, for example from xe2x80x9cLexikon der Optik,xe2x80x9d H. Haferkorn, Ed., Hanau: Dausien 1988, pp. 342, to arrange a lens system as a beam converter for the spatial shaping of the beam. The arrangement of an additional lens system has the drawback that the technical complexity that is required to shape the cross section of the laser beam is high.
It is an object of the invention to provide a laser with an improved integrated optical beam converter.
Another object of the invention is to provide a laser with an integrated optical beam converter that is characterized by small overall size and simplified, cost-effective design.
These and other objects of the invention are achieved by providing an apparatus for frequency conversion of laser light comprising at least one non-linear crystal arranged in a laser beam and into which the required power density is introduced by an arrangement in the area of the focal point of an associated focusing lens system, the apparatus comprising a collimator that minimizes divergence of the laser beam and an optical beam converter that shapes the laser beam cross section, wherein the collimator is formed by a correction lens, and means are provided to change the angular position of the correction lens by an angle xcex8 relative to the laser beam such that the correction lens additionally acts as an optical beam converter.
Further preferred embodiments of the invention are described and claimed hereinafter.
The fact that the collimator is formed by a correction lens and means are provided to change the angular position by an angle xcex8 relative to the laser beam makes it possible for the correction lens in addition to act as an optical beam converter. Thus, it is possible to adapt the cross section of the laser beam to different requirements or to adjust the device with minimum complexity. Furthermore, a small overall length and a significant simplification of the technical design are achieved.
A preferred embodiment comprises two crystals arranged in the laser beam, one directly behind the other. Their geometric center is in or near the point of the focusing lens making it possible here again to introduce the required power density. Thus, even if two crystals are arranged, only a single focusing lens system is required. Moreover, an additional collimator is eliminated.
It is furthermore advantageous if the correction lens is a spherical lens. This makes it possible to use the astigmatism of the lens to shape the desired cross section of the laser beam even by means of small corrections in the angular position of the correction lens relative to the optical axis.
Preferably, the correction lens is supported in an inner ring, which is rotatable about an axis relative to the optical axis by an angle xcex8. This inner ring with its axis is preferably mounted within an outer ring that can be azimuthally rotated by an angle xcfx86. A construction of this type makes it possible to align the correction lens exactly in the beam path at any angle relative to the optical axis to form the cross section of the laser beam.